EDIT2: furthermore i am even unsure about this whole shader as it seems to even work if you remove some of the setShader things... alas, shaders forever in mystery, it's like few people seem to understand them!

I modified it to work full screen and you're right; it's generally too blurry and dark. It can be sharpened up but at the cost of losing the shadow mask effect, which is mainly what I'm after in a CRT shader.